If this can be fake and not realistic I would mix laser printer warm up with scanner sounds and high speed washing mashine spinning, maybe some electric gentle sparks. Maybe add some mechanic moving sounds taken from rewinding slowed tape. That is common image of how it can sound - in reality i suppose the sound is not attractive.

On the realistic perspective, here's what you would expect:A patient being scanned is put on a strecher that is moved inside the machine (you woul have an electri motor sound here lasting a few seconds as the whole stretcher is moved into the machine).Then there would probably be a beep signaling the start of the scan. Followed by a slower electric motor noise as the sensor or the strecher are moved so the whole body of the patient is scanned.

The scanning element itself should emit no noise, but larege magnetic fields are involved, so you may want to add a humm type of sound.Finally, another beep and the stopping of the motor should mark the end of the scan.After a pause the motor would go again to pull the strecher out of thr rmn scanner.

An important thing to bear in mind is how you want all of these sounds to be perceived? As if you were being put inside the machine? Or as if you are just in the room?If going inside the machine, the motor sound would feel very close. As you go in, the outside sounds would become muffled, and the motor and the humm sound would have the feel of an enclosed space. This can be done with EQ, and preferably by putting the sounds through a convolution reverb for a very small space.

If outside, consider adding an air conditioning noise. The rooms where these machines sit are usually fairly large and unnimpeded. Consider a convolution reverb for a large empty room.

I'm making a Matrix like radio play as a present, and building a sound for a positioning a scanner above the head.I found a great sound for positioning the scanner: elevator_motor.wav bij searhing for "elevator".I increased the speed for 40% en cut 50% of the piece in the middle.

I mix it with sound marcus-obst-unterbecken-07.2005.ogg and filter the high and low frequences away. You can find it by searching "unterbecken".